1. Field of the Invention
The present invention relates to a technology for making it more difficult to listen to a portion of a sound output from a speaker.
2. Description of the Related Art
Recently, it is possible to use a display that is connected via a communication network to a monitoring camera installed at a remote location to view video captured by the monitoring camera. Further, if the monitoring camera has a microphone, it is also possible to use a speaker connected via the communication network to the microphone to listen to a sound recorded by the microphone.
Specifically, a viewer can realistically and richly see and hear what is happening at that remote location based on information acquired by the monitoring camera and the microphone installed at the remote location.
However, the sound recorded by the microphone may include a person's voice. Thus, if the viewer is allowed to listen to the recorded sound as is, the viewer may learn of personal information or confidential information regardless of the wishes of the person who is speaking.
Accordingly, a technology has been proposed which makes it more difficult to identify speech contents by attenuating the respective peaks (hereinafter, “formants”) in a spectral envelope obtained when a spectrum constituting an audio signal, such as a person's voice, is plotted along the frequency axis (for example, see Japanese Patent Application Laid-Open No. 2007-243856).
Although the technology discussed in Japanese Patent Application Laid-Open No. 2007-243856 enables most of the sounds from the remote location to be perceived, this technology makes it more difficult to identify the speech contents represented by the person's voice included in the sound recorded by the microphone that can be clearly identified.
However, for example, if the viewer adjusts the speaker volume and listens carefully, among the people's voices included in the sound recorded by the microphone, the speech contents of voices that, although not clearly, can be barely identified might be identifiable.